There's nothing to "add". It's either a separate single-app plan or you go big with the full CC.
Yeah, once you add a second app, you might as well just get the full CC. That way you have Photoshop and Illustrator too (both very helpful for AE work), Audition (great for doing audio work), and all of the other nice CC stuff. I really like the mobile apps and their integration with the rest of the suite - especially Capture. Do you get all the free fonts and free assets in the CC app with a single app subscription? You do with a full subscription and I find that stuff really useful.